9th ECCC European Continuous Casting Conference – ECCC 2017

In some cases, the precipitation of CaS around CaO-Al2O3 inclusions are observed in hot coil, even though it is not found in CC slab. The purpose of this study is to investigate S solubility in solid CaO-Al2O3 at various temperatures and clarify the mechanism of this phenomenon. For the experiment, first, the mixture of the reagent of CaO, Al2O3, CaS at a given composition was charged in Al2O3 or Pt crucible. Then, the CaO-Al2O3-CaS oxides were melted at 1723K in Ar atmosphere. After that, the oxide sample was cooled and kept at around 1173K for 1 hour and quenched. The obtained oxides were analyzed by FE-EPMA. In the sample of 42.2CaO-51.5Al2O3-6.3CaS(mass%), 12CaO･7Al2O3(C12A7), CaO･Al2O3(CA) and CaO･2Al2O3(CA2) were observed and in the sample of 51.5CaO-42.2Al2O3-6.3CaS(mass%), C12A7 and 3CaO･Al2O3(C3A) were observed. In every condition, sulfur content in C12A7 showed extremely high but its content in the other oxides were close to zero. The solubility of sulfur in C12A7 was around 1.2% and was independent on heating temperature. This value was higher than the sulfur solubility in the molten oxide of CaO-Al2O3 just above its melting point. This result indicates that by the control of oxide composition, the precipitation of CaS around the oxide is able to be avoided.